Conventionally, an engine is often employed as a drive source of a portable working machine such as a chain saw and a brushcutter. As a matter of course, the engine is equipped with a silencing muffler. The muffler is typically attached to an engine body by multiple bolts that penetrate a muffler body. In addition, the muffler is sometimes provided with a baffle (also called a partition cylinder) for improving the strength of portions of the muffler body where the bolts are fastened and for changing a flow direction of an exhaust gas to a predetermined direction immediately after the exhaust gas has entered the muffler body (e.g., Patent Document 1).
The baffle disclosed in Patent Document 1 not only covers the exhaust port provided to the muffler body but also partitions the muffler chamber, so that the exhaust gas from the engine enters a space covered by the baffle and then is flowed to the muffler chamber through multiple holes perforated at predetermined positions in the baffle.    Patent Document 1: JP-UM-A-32737